The present invention relates generally to signaling protocols for wireless communication systems, and more particularly, to a method of reducing the size of signaling messages transmitted over a wireless communication link.
The Session Initiation Protocol (SIP) and the Session Description Protocol (SDP) are becoming the de facto standards for IP telephony. SIP is a text-based protocol used for setting-up, modifying, and tearing down media sessions. SIP has also been extended for instant messaging and presence services. SDP is a text-based signaling protocol for describing multimedia sessions. SDP is used for purposes such as session announcement, session invitation, and other forms of multimedia session initiation.
SIP and SDP were originally designed for rich bandwidth connections, so message sizes are not optimized and tend to be rather large. The relatively large message size of SIP messages causes some difficulties when SIP signaling must traverse a narrow bandwidth connection, such as a radio interface in wireless networks or a low-speed serial connection. The large message size of SIP messages consumes valuable bandwidth in wireless networks and substantially increases call set-up time.
The Internet Engineering Task Force (IETF) has developed a signal compression protocol known as SIGCOMP to reduce the size of SIP messages for transmission over limited bandwidth connections. The SIGCOMP protocol is described in IETF documents RFC 3320 and RFC 3321, which are incorporated herein by reference. The SIGCOMP protocol makes use of compression/decompression engines at the sending and receiving nodes. The sending node compresses SIP messages and sends the compressed messages to the receiving node along with decompression code needed to decompress the message. Because decompression code is passed from the sender to the receiver, software SIP clients can implement virtually any known compression algorithm and remain compatible with other SIP clients.